These days, toners need to have a smaller particle size for higher quality of output images, high temperature off-set resistance, low temperature fixing properties for energy saving, and heat-resistant preservation properties meaning endurance under a high temperature and high humidity environment during preservation and transportation of the toners. Especially the power consumed during fixing constitutes a large part of the total power consumption in the image forming method, and it is very important to improve the low temperature fixing properties.
Toners produced by a kneading pulverization method have been used. In this method, a colorant, a mold release agent, and the like are melted and mixed in a binder resin and uniformly dispersed to prepare a toner composition, and the toner composition is ground and classified to produce a toner. The toner produced by the kneading pulverization method is difficult to attain a reduction in the particle size. Additionally, the toner has an amorphous shape and a broad particle size distribution, leading to insufficient quality of an output image and high fixing energy. When a mold release agent (wax) is added to improve fixing properties, the toner produced by the kneading pulverization method will crack at the interface of the wax in grinding, and a large amount of the wax will exist on the toner surface. For this reason, although a release effect is attained, the toner will adhere to a carrier, a photoconductor, and a cleaning blade (filming), leading to unsatisfactory total performance of the toner.
To solve the above problems of the toner produced by the kneading pulverization method, various methods for producing a toner by a polymerization method have been proposed. The toner produced by the polymerization method has a smaller particle size and a sharp particle size distribution, enabling encapsulation of the mold release agent.
An exemplary method for producing a toner by the polymerization method is proposed in which to improve low temperature fixing properties and high temperature off-set resistance, a toner is produced from an elongation reaction product of a urethane-modified polyester (see PTL 1).
Toners having a smaller particle size are proposed having excellent powder fluidity and transfer properties and excellent heat-resistant preservation properties, low temperature fixing properties, and high temperature off-set resistance (see PTLs 2 and 3).
Toner production methods are proposed including a step of producing a toner binder having a stable molecular weight distribution and an aging step for attaining low temperature fixing properties and high temperature off-set resistance at the same time (see PTLs 4 and 5).
These proposed techniques, however, cannot provide a higher level of low temperature fixing properties which are demanded these days.
To attain a higher level of low temperature fixing properties, a toner is proposed, the toner including a resin (a) having no polyhydroxycarboxylic acid skeleton of an photoactive monomer and a resin (b) having a polyhydroxycarboxylic acid skeleton of a photoactive monomer, wherein the resin (a) is a crystalline polyester resin (see PTL 6), for example.
Another toner is proposed, the toner including a core of a block copolymer having a crystalline polyester block and a non-crystalline polyester block and an outer shell of a non-crystalline polyester resin (see PTL 7).
According to these proposals, the toner can attain low temperature fixing properties because the crystalline polyester resin melts faster than the non-crystalline polyester resin. While the crystalline polyester resin as the island in the sea-island phase separated structure is melted, the non-crystalline polyester resin as the sea occupying most of the structure is not melted yet. The fixing is attained when both the crystalline polyester resin and the non-crystalline polyester resin are melted to a certain degree. Consequently, these proposed techniques cannot provide a higher level of low temperature fixing properties.
Accordingly, it is desired to provide a toner having excellent low temperature fixing properties, high temperature off-set resistance, and heat-resistant preservation properties without producing filming.